The invention relates to a device for analysis of problems with the balance, and strategies for postural regulation of a person.
It is universally recognised at present by the medical profession that analysis of problems with balance is an excellent tool in particular for assessing and objectifying dysfunctioning of the main neuro-motive and sensorial systems, and also for evaluating the efficiency of rehabilitation therapy of these same systems.
For these reasons, scientists and doctors have developed devices and methodologies for carrying out this analysis. These techniques as a whole are known as clinical posturology, and are aimed at permitting thorough, reliable analysis of the posture of a person in static and dynamic positions.
For this purpose, at present, equipment developed consists of computerised posturology platforms, which make it possible to measure and record the displacement of the centre of pressures of the feet of a person in different examination conditions, which displacement is a direct consequence of the oscillations of the body, which themselves are derived from the quality of regulation of the different neuro-sensorial and neuro-motive systems.
The purpose of the platforms most commonly used is to make it possible to evaluate quantitatively the spontaneous movements of the body of a person in an orthostatic position on a stable base.
For this purpose, the platforms generally consist of static force platforms, comprising a non-deformable stand, which is supported on rigid sensors (strain gauges), which make it possible to analyse the vertical component of the resulting force applied by the weight of the body of a person on the said platforms.
Platforms of this type, connected to a micro-computer, make it possible in particular to provide a plurality of parameters (average X, average Y, length, surfaces, fast FOURIER transformations) which take into account the performance of a person to be kept upright at a given moment, and make it possible to assess the quality of his sensory-motor regulation loops.
The parameters obtained by means of static platforms of this type have proved to be insufficient, owing to the fact that, in everyday life, a patient is rarely in a situation of static balance. For this purpose, and in order to complete the results obtained by means of the static platforms, unstable platforms have been developed, which permit displacements of the sustentation polygon, under the effect of the physiological movements of balancing of the patient, which are thus independent from any external motorisation.
A first type of mobile platform used at present consists of a stand which is supported on a swivel joint or on a shaft (SINGER, BACHMAN, BEGBIE platforms, etc). However, it has been found that when a patient is in place on platforms of this type, his balance is too unstable, and, consequently, he is in danger of falling. Furthermore, maintenance of balance of this type of platform is impossible for pathological patients.
In practice, and for these reasons, mobile platforms of this type are equipped either with stops for limitation of the inclination of the platform, or with a brake, a shock absorber or a spring for slowing down the movement, in order to prevent the patient from falling.
However, the set of stops fragments the continuity of the measurement, and the use of brakes, shock absorbers or springs detracts from the reproducibility of the examination, such that the results obtained by means of platforms of these types are difficult to use, and in no case represent proof of dynamic physiological balance.
In order to eliminate these disadvantages, and to obtain dynamic balance measurement parameters which are easy to compare, one solution consists of providing a mobile platform which creates a spontaneously unstable situation of balance, consisting of a platform, beneath which there is secured a portion of cylinder.
According to this principle, the assembly is supported on the ground by means of a generatrix of the cylinder, and forms a platform with a single degree of freedom of movement. The variation of inclination imposed by the patient in order to maintain his balance is picked up by means of an inclinometer or accelerometer, which provides directly the angular position of the platform relative to the horizontal, which datum is acquired and processed by a micro-computer.
A mobile platform of this type thus permits development by the patient of simple, efficient balance reactions, consisting of rotation associated with translation of the patient on the platform.
Owing to its simplicity, its ease of application, the possibility of distinguishing frontal balance and sagittal balance, and the many parameters which can be exploited, as a complement to static platforms, a mobile platform of this type has been found to constitute an excellent means for evaluation of problems with balance, for objective monitoring of the results of medical or surgical therapy, and for guiding of physiotherapy.
The object of the present invention is also a device comprising a mobile platform as previously described, and its main objective is to provide a device which is equipped with a platform of this type, which firstly makes it possible to carry out the analysis of the posture of a person, both in orthostatic and dynamic conditions, and secondly, the cost price of which is only slightly higher than that of a static platform alone.
Another object of the invention is to provide a device for analysis which makes it possible to gather an increased number of parameters in dynamic conditions, relative to those gathered by means of the present mobile platforms, and which differentiates the strategies for balancing on the sagittal plane, from the strategies for balancing on the frontal plane.
For this purpose, the invention relates to a device for analysis of the posture of a person, comprising:
a static force platform which is provided with sensors, which can emit signals which are representative of the position and absolute value of the forces exerted on the said platform by a person in a position of orthostatic balance;
a mobile platform, which is placed on the static platform, and consists of a stand which is secured to means for support, which have a lower support surface in the form of a cylindrical section, the area of contact of which with the static platform consists of one of the generatrices of the said lower support surface, which forms the pivot of the said mobile platform; and
a unit for acquisition and processing of the signals emitted by the sensors of the static platform, programmed in order to acquire the said signals with a pre-determined frequency, and to proceed with an analysis of the problems with balance and posture of the person, according to frontal and sagittal balance planes, and with frequential analyses of the oscillations created, such as to define the contribution of the different sensory-motor regulation loops, towards maintaining balance in dynamic conditions.
Unlike all the present solutions, which make it necessary to carry out the analyses in orthostatic and dynamic conditions by means of different platforms, each of which is provided with its own measuring sensors and its own unit for acquisition and processing, the invention consists of using the potential provided by the static platforms, such that the latter act as means for measurement which make it possible to evaluate the variations of inclination which a person imposes on a mobile platform, in conditions of dynamic balance.
For an additional cost in relation to a static platform, which corresponds to the cost of a simple mobile platform, the device for analysis according to the invention thus makes it possible to analyse the posture of a person in orthostatic conditions, using the static platform alone, and in dynamic conditions, by placing the mobile platform on the said static platform.
In addition, since the mobile platform is positioned on a static platform, the sensors of the latter make it possible to record not only the variations of the inclination of the said mobile platform, but also the transfers of support, according to an axis which is parallel to the axis of the pivot. Thus, numerous parameters can be exploited in order to take into account performance of balance of a patient, such as:
the length of the path of balance, expressed in mm, degrees or radians;
the maximum amplitude of the oscillations, expressed in mm, degrees or radians;
the average position of the mobile platform, around which the patient is balanced, expressed in mm, degrees or radians;
the vectorial components according to two axes x, y, which are respectively parallel and at right-angles to the axis of the pivot, of the path of balance, which are calculated and represented according to the time (stabilogram at x, and stabiligram at y).
These parameters quantify the ability of the patient to balance in dynamic conditions.
Other parameters also make it possible to take into account individual balance strategies, and to assess the relative contribution of the sensory-motor regulation loops, towards maintaining the balance of the patient.
These parameters are obtained by carrying out a frequential analysis of each stabilogram, by frequency bands, i.e. by calculating the spectral energy of the oscillations, with indication of the distribution of this energy by frequency bands, and as a percentage of the total energy.
With reference to these frequency bands, and advantageously, the unit for acquisition and processing is programmed to proceed with frequential analyses of the oscillations, and their objectivation in three frequency bands, i.e. a band of 0 Hz to 0.5 Hz, a band of 0.5 Hz to 2 Hz, and a band of 2 Hz to 20 Hz.
In fact, the band of 0 to 0.5 Hz corresponds to the slow regulation loops, with a visual and vestibular starting point. The band of 0.5 to 2 Hz corresponds to the regulation loops which are associated with the cerebellar integration. Finally, the band of 2 Hz to 20 Hz corresponds to the fast regulation loops, which are associated with the myotactic reflexes.
According to an advantageous embodiment, the unit for acquisition and processing is programmed in order to acquire the signals emitted by the sensors of the static platform, with a frequency of 40 Hz or more. In fact, frequencies of acquisition of this type make it possible to obtain ideal spectra in a frequency band of 0 to 11 Hz, this last value constituting the fastest physiological trembling of a human being.
In addition, the device according to the invention can be used not only with a patient in a standing position, for the purpose of measurement of his frontal balance and sagittal balance, but also with a patient in a seated position, by positioning and securing the static platform on a support such as a stool.
In this case, in addition, and advantageously, the device comprises a seat with an anatomical shape, the said seat and the mobile platform being provided with means for relative positioning of centring and maintenance of the seat on the mobile platform.
In addition, advantageously, the means for relative positioning of the seat and of the platform comprise a central aperture which is provided in the stand of the said mobile platform, and a centring rod which is secured beneath the said seat, and has a cross-section suitable for being accommodated in the aperture of the said stand.
In addition, according to an advantageous embodiment, the means for support of the stand of the mobile platform consist of two arches with a circular section, disposed laterally beneath the said stand.